Golf club head

ABSTRACT

A face member of a golf club head includes first and second main ribs disposed inside thereof. The first main rib is extended from a crown side to a sole side and the second main rib is extended from a hosel side to a toe side of the sole. The first and the second main ribs intersect with each other at an intersection portion. Additionally, a first groove is provided from the intersection portion of the rib toward the sole side, and a second groove is provided from the intersection portion of the rib toward the toe side.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority on Japanese Patent Application No. 2010-205523 filed on Sep. 14, 2010, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf club head, and more particularly relates to a golf club head in which improvement is made by providing a back side of its face portion with thick portions.

2. Description of Related Art

In most of the recently marketed wood club heads, at least a face portion thereof is formed of metallic material. The face portion must be so thick so as to maintain strength capable of withstanding an impact with a ball. Although the size of the head has been currently tending to increase, large heads of 460 cm³, which is an upper official limit according to a golf rule, take up most of the driver head share because the driver heads must be formed in a smaller volume than 460 cm³+an allowance of 10 cm³.

If the head size is expanded, the weight of the face portion is increased. Thus, generally, while reduction of weight of the face portion has been attempted, the thickness of a face portion has been decreased in order to maintain the strength of the face portion and a measure of providing a back side of the face portion with ribs has been adopted. For example, Japanese Unexamined Patent Application Publication No. 2006-141806 has described provision of six ribs extending from a central portion of the face toward a periphery of the face.

If a rib is provided in the shape of the letter X on the central portion of a back surface of the face portion, restitutive performance of the face portion drops drastically when a ball is hit on a sole side or a crown side off a face center, as compared to a case in which a ball is hit on the face center. To solve this problem, Japanese Unexamined Patent Application Publication No. 2008-36050 has described that the thickness of four division faces on the back side of the face, which are defined by dividing with the ribs is so determined that those on the sole side and the crown side are smaller than those on the toe side and the heel side.

Conventionally, a number of highly restitutive heads whose coefficient of restitution was increased considerably were invented. However, it has been officially decided that highly restitutive heads whose coefficient of restitution is 0.830 or more cannot be used in games from 2008 on. Accordingly, there have been currently developed golf clubs whose coefficient of restitution at a center of its face portion is suppressed. However, it has been made evident that if the coefficient of restitution at the center of the face portion is suppressed, the restitutive performance of a face surface other than the center is lower on the sole side than on the crown side.

SUMMARY OF THE INVENTION

In view of the above-described problem, accordingly, an object of the present invention is to provide a golf club head in which with the weight of its face portion is reduced and the strength of its face portion is maintained, the restitutive property of its face center is held within a range complying with golf rules, and even if a ball is hit off the face center, substantially the same restitutive performance as when the ball is hit at the face center can be exerted.

To achieve the above-described object, according to the present invention, there is provided a golf club head having a hollow internal structure, the golf club head including: a face portion having a hitting surface; and first and second main ribs disposed inside the face portion. The first main rib is extended from a crown side to a sole side and the second main rib is extended from a hosel side to a toe side of the sole, and the first and second main ribs intersect with each other at an intersection portion. Additionally, the first and the second main ribs are so constructed that stiffness of the sole side is lower than that of the crown side.

According to another embodiment of the golf club head, a first groove is provided from the intersection portion of the first main rib up to the sole side, and the depth of the first groove is ¾ or less the maximum height of the first main rib. Furthermore, a second groove is provided from the intersection portion of the second main rib up to the toe side, and the depth of the second groove is ¾ or less the maximum height of the second main rib.

According to another embodiment of the present invention, the height of the first and second main rib is 0.5 mm to 1.5 mm.

According to another embodiment of the golf club head, the height of the first and second main ribs is less on the sole side than on the crown side.

According to another embodiment of the present invention, the width of the first and second main ribs is 8 mm to 14 mm.

According to another embodiment of the present invention, the golf club head further includes a reinforcement rib which is disposed inside the face portion and extended from the intersection portion toward an end of the face portion. The height of the reinforcement rib decreases gradually from the intersection portion toward the end, and the same reinforcement portion is formed part of the way to the end of the face portion.

The golf club head of the present invention has a hollow internal structure and includes a face portion having a hitting surface and first and second main ribs disposed inside the face portion. Then, the first main rib is extended from a crown side to a sole side and the second main rib is extended from a hosel side to a toe side of the sole. The first and second main ribs intersect with each other at an intersection portion. The first and the second main ribs are so constructed that stiffness of the sole side is lower than that of the crown side. According to the structure of such a golf club head, a light weight face portion can be formed and a sufficient strength of the face portion can be maintained, while restitutive property of the face center can be kept within a rule complying range. Additionally, restitutive performance when a ball is hit off a face center is brought close to the same restitutive performance as when the ball is hit at the face center.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1(A) is a front view showing an embodiment of a golf club head according to the present invention;

FIG. 1(B) is a front view showing another embodiment of the golf club head according to the present invention;

FIG. 2 is a sectional view of the golf club head taken along the line II-II in FIG. 1(A);

FIG. 3 is a back side view showing a face member constituting the golf club head shown in FIG. 1(A);

FIG. 4 is a schematic sectional view of the face member taken along the line IV-IV in FIG. 3;

FIG. 5 is a schematic sectional view of the face member taken along the line V-V in FIG. 3;

FIG. 6 is a front view showing angles of ribs on the face member in FIG. 1(A);

FIG. 7 is a sectional view showing another embodiment of a groove provided in the rib;

FIG. 8 is a sectional view showing still another embodiment of the groove provided in the rib;

FIG. 9 is a sectional view showing another embodiment of the groove in the rib;

FIG. 10 is a sectional view showing another embodiment of the groove provided in the rib;

FIG. 11 is a front view showing another embodiment of the golf club head according to the present invention;

FIG. 12 is a schematic sectional view of a rib according to a comparative example;

FIG. 13 is a front view showing hitting points in simulations of examples;

FIG. 14 is a distribution diagram of CT values of an example 1-1;

FIG. 15 is a distribution diagram of the CT values of an example 1-2; and

FIG. 16 is a distribution diagram of the CT value according to a comparative example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of a golf club head according to the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1(A) and FIG. 2, a golf club head 1 is constituted mainly of a face member 11 a which is part of a face portion 10 and a main body member 20. The main body member 20 includes part of the face portion 10, a sole portion 21, a crown portion 22, a side portion extending from a toe 23 to a heel 24 via a back face (not shown) and a hosel portion 25, which are formed integrally. The face member 11 a and the main body portion 20 are joined together by welding, so that a hollow structure is formed inside the head.

Preferably, the face member 11 a contains at least a sweet spot in the face portion 10. Preferably, the width of the face member 11 a is about 55% or more the width of the face portion 10, more preferably about 60% or more. Furthermore, the width of the face member 11 a is preferably about 90% or less the width of the face portion 10 and more preferably to be about 85% or less. The height of the face member 11 a is preferably about 50% or more the height of the face portion 10 and more preferably to be about 55% or more. Furthermore, the height of the face member 11 a is preferably about 90% or less the height of the face portion 10 and more preferably about 85% or less. Preferably, outer edges on the toe side and the heel side of the face member 11 a are substantially parallel to a central axis 31 of a first main rib 12, which will be described later. Preferably, the main body member 20 has a toe side portion 26 of the face portion and a heel side portion 27 thereof.

FIG. 1(A) indicates a structure of a face on the hollow structure side of the face member 11 a, namely, a back side face by the broken line. Ribs are formed on the back side face of the face member 11 a by intensifying the thickness of the face member 11 a partially.

In the meantime, the face member of this embodiment is not limited to the face member 11 a which is to be fit to a U-shaped opening portion made in part of the face portion 10, but the entire area of the face portion 10 may be used as the face member 11 b as shown in FIG. 1(B). Then, main ribs 12, 13 may be provided on the entire face portion 10. In this case, the main rib 12 is extended up to the vicinity of an outer periphery on the sole side of the face portion 10. The main rib 13 is extended from the vicinity of the outer periphery on the hosel side of the face portion 10 up to the vicinity of the outer periphery on the toe side. Because the main ribs 12, 13 are not extended up to ends of the outer periphery of the face portion, the face member may be fit easily to a crown front end portion and a sole front end portion where the opening portion of the face portion is made. Next, the back side face of the face member 11 a shown in FIG. 1(A) will be described.

As shown in FIG. 3, the first main rib 12 extending from the sole side to the crown side and the second main rib 13 extending from the hosel side to the toe side of the sole are formed on a substantially flat back side face of the face member 11 a. The first and second main ribs 12, 13 intersect with each other at a flat circular intersection portion 15 disposed on a sweet spot of the face portion 10. Intersection of the first and second main ribs 12, 13 at the central portion of the face portion 10 suppresses restitutive performance at the central portion of the face portion 10.

A first groove 50 is provided in a sole side portion of the first main rib 12 as viewed from the intersection portion 15 along the longitudinal direction of the same rib 12. Furthermore, a second groove 51 is provided in the sole side portion of the second main rib 13 as viewed from the intersection portion 15 along the longitudinal direction of the same rib 13. Provision of the first groove 50 and the second groove 51 can reduce stiffness of the sole side portion of the ribs 12, 13 thereby increasing restitutive performance on the sole side of the face portion up to a substantially equivalent level to the restitutive performance on the crown side.

The back side face of the face member 11 a is divided into four sections, toe-crown section 16, toe-sole section 17, heel-crown section 18 and heel-sole section 19 by the first main rib 12 and the second main rib 13. The thickness of the face member 11 a is defined to differ across the first main rib 12. That is, the thickness of the toe-crown section 16 and the toe-sole section 17 is defined to be smaller than the thickness of the heel-crown section 18 and the heel-sole section 19. Defining the thickness of the face member 11 a such that the thickness on the toe side is smaller than that on the heel side intensifies the restitutive performance on the toe side, so that the restitutive performance on the toe side comes close to the restitutive performance on the heel side.

Additionally, a reinforcement rib 14 extending from the toe-crown section 16 to the heel-sole section 19 is formed on the back side face of the face member 11 a. The reinforcement rib 14 intersects with the first and second main ribs 12, 13 at the intersection portion 15. In the meantime, the reinforcement rib 14 is formed only part of the way to an end of the face portion. By forming the reinforcement rib 14 in case in which the restitutive performances of the toe-crown section 16 and the heel-sole section 19 exceed a golf rule complying range, the same reinforcement rib 14 can suppress the restitutive performance of these sections.

The reinforcement rib 14 may contain a third groove 52 on its sole side with respect to the intersection portion 15, along the longitudinal direction of the same rib 14. Provision of the groove 52 in the reinforcement rib 14 may adjust the restitutive performance of the face portion by reducing stiffness of the reinforcement rib 14. Respective parts on the back side face of the face member 11 a will be described in more detail.

As shown in FIG. 4, the first main rib 12 is so constructed that the first groove 50 is provided near the center of a top side of its substantially trapezoidal formation. The section of the first groove 50 is rectangular. The height of the first main rib 12 may be defined to be decreased gradually toward the flat toe-sole section 17 and heel-sole section 19. As shown in FIG. 4, the thickness of the toe-sole section 17 is defined to be smaller than the thickness of the heel-sole section 19. As a result, on the sole side of the face portion, the coefficient of restitution can be intensified on the toe side as compared to the heel side. This sectional view is intended to make the structure of the present invention understood easily, but it is not drawn to scale. The first main rib 12 is formed in an equal height from the intersection portion 15 toward an outer edge of the face member 11 a. The height of the second main rib 13 is defined in the same manner as the first main rib 12.

The height of the first main rib 12 refers to a largest difference T_(R) in thickness between the top of the rib and the surface of a section 19 which is thicker than a neighboring section. The T_(R) is preferably about 0.5 mm or more and more preferably about 0.7 mm or more. Furthermore, the T_(R) is preferably about 1.5 mm or less and more preferably about 1.2 mm or less. Then, a depth T_(G) of the first groove 50 is preferably smaller than T_(R) and T_(G) is more preferably ¾ or less T_(R). The height of the second main rib 13 is equal to that of the first main rib 12 and the depth of the second groove 51 is equal to that of the first groove 50. The first and second main ribs 12, 13 are preferably formed up to an end of the face member 11 a or the vicinity thereof. The first and second main ribs 12, 13 are formed each in a substantially equal width. The width of the first and second main ribs 12, 13 is preferably about 8 mm or more at their portions in contact with the back side face of the face portion and more preferably about 9 mm or more. The width of the first and second main ribs 12, 13 is preferably about 14 mm or less and more preferably about 13 mm or less.

The configuration of the first groove 50 has been already described above. The configurations of the second groove 51 and the third groove 52 are similar to that of the first groove 50.

The reinforcement rib 14 is so constructed that like the main ribs, the height of its central portion is the greatest and the height thereof decreases gradually from the central portion toward the flat toe-crown section 16 and heel-sole section 19. On the other hand, as shown in FIG. 5, the height of the reinforcement rib 14 is defined so as to decrease gradually from the intersection portion 15 toward the outer edge of the face member 11 a. In the meantime, this sectional view is not drawn to the scale. Additionally, the width of the reinforcement rib 14 is defined so as to decrease gradually from the intersection portion 15 toward the outer edge of the face member 11 a. Forming the reinforcement rib 14 to be gradually thinner and narrower from the center thereof toward the outer edge can suppress a quick change in stiffness.

A length of the reinforcement rib 14 from the intersection portion 15 is preferably about 45% or more and more preferably about 50% or more a length from the intersection portion 15 up to the outer edge of the face member 11 a. Furthermore, it is preferably about 90% or less and more preferably about 85% or less. The length on the toe side and the length on the heel side may be equal to or different from each other. Although the height of the highest portion of the reinforcement rib 14 is preferably equal to the height of the highest portion of the first and second main ribs 12, 13, it may be lower than the first and second main ribs 12, 13. In case in which it is lower, the difference is preferably about 0.1 mm or more and about 0.5 mm or less. The width of the reinforcement rib 14 is preferably about 2 mm or more at its greatest portion and more preferably about 3 mm or more. Furthermore, the width of the reinforcement 14 is preferably about 12 mm or less and more preferably about 10 mm or less.

On the crown side, the first main rib 12 is preferably inclined toward the toe side, and on the sole side, toward the heel side. Inclination of the first main rib 12 in this way can extract restitutive performance along a direction from the toe upper side to the heel lower side, where hitting points by amateur golfers concentrate, to a maximum extent. More specifically, an angle θa of a center line 31 of the first main rib 12 with respect to a ground line (G.L) 30 when the golf club head 1 is placed on an ordinary address position as shown in FIG. 6 is preferred be about 90° or less and more preferably about 85° or less. Furthermore, the inclination θa of the rib is preferably about 25° or more and more preferably about 30° or more.

On the toe side, the second main rib 13 is preferably inclined toward the sole side and on the heel side, toward the crown side, that is, toward the hosel side. Inclination of the second main rib 13 in this way can extract restitutive performance in an upward direction at the toe to a maximum extent. More specifically, an inclination θb of a center line 32 of the second main rib 13 with respect to the ground line 30 is preferably about 5° or more and more preferably about 10° or more. Furthermore, the inclination θb of the rib is preferably about 80° or less and more preferably about 70° or less. Preferably, a center line 33 of the reinforcement rib 14 divides an angle formed by both the center lines 31, 32 of the first and second main ribs 12, 13 respectively into two equal parts.

By curving the first main rib 12 smoothly into an S-shape or Z-shape instead of the straight line along the center line 31 and by curving the second main rib 13 smoothly into an S-shape or Z-shape instead of the straight line along the center line 32, areas of both the toe-crown section 16 and the heel-sole area 19 can be increased. The reinforcement rib 14 is preferably of a straight line along the center line 33.

The toe-crown section 16, the toe-sole section 17, the heel-crown section 18 and the heel-sole section 19 each have a substantially uniform thickness. To equalize the coefficient of restitution of the toe side with that of the heel side, the thickness of the toe-crown section 16 can be made less than the thickness of the heel-sole section 19. Furthermore, the thickness of the toe-sole section 17 can be made less than the thickness of the heel-crown section 18. Preferably, a difference of these thicknesses is at least about 0.05 mm or more, more preferably about 0.1 mm or more. On the other hand, no uniform restitutive performance can be obtained if the difference of these thicknesses is excessive. Thus, it is preferably about 0.5 mm or less, and more preferably about 0.4 mm or less.

Although the thickness of the toe-crown section 16 may be equal to or different from the thickness of the toe-sole section 17, preferably, the thickness of the toe-sole section 17 is made less than the thickness of the toe-crown section 16 in order to equalize the coefficient of restitution of the crown side with that of the sole side as much as possible. A difference of these thicknesses is preferably about 0.05 mm or more, and more preferably about 0.1 mm or more. On the other hand, no uniform restitutive performance can be obtained if the difference of these thicknesses is excessive. Thus, it is preferably about 0.5 mm or less and more preferably about 0.4 mm or less.

The thickness of the heel-crown section 18 and the thickness of the heel-sole section 19 may be equal to or different from each other. When defining the thickness of the heel-crown section 18 to be different from the thickness of the heel-sole section 19, the difference of the thickness is preferably about 0.05 mm or more and about 0.5 mm or less.

The intersection portion 15 contains the sweet spot of the face portion 10, that is, a center of gravity of a golf club head projected to the face plane. The intersection portion 15 contains an intersection point of the center lines of the first and second main ribs 12, 13. The intersection point of the main ribs and the sweet spot may be equal to or different from each other. The intersection point of the main ribs 12, 13 is disposed so as not to be on a score line formed on the surface of the face portion 10 or so as not to be on an extension line of the score line 28 formed partially on the toe side and the heel side, as shown in FIG. 1.

Although the height of the intersection portion 15 is preferably the same as that of the highest portion of the first and second main ribs, it may be greater. In a case in which the height of the intersection portion 15 is set to be greater than that of the main ribs, a difference of those heights is preferably about 0.1 mm or more and about 0.5 mm or less. The surface of the intersection portion 15 is preferred to have a circular section, and as shown in FIG. 5, the section of the intersection portion 15 has a substantially semicircular or substantially semielliptical shape. The radius of the flat, circular intersection portion 15 is preferably about 5 mm or more and about 12 mm or less at its widest portion. In addition, the intersection portion 15 is not limited to the circular shape, and it may be elliptical, square, such as rectangular and diamond shaped, or polygonal such as pentagonal and hexagonal.

Although the toe-crown section 16, the toe-sole section 17, the heel-crown section 18 and the heel-sole section 19 have the above-mentioned difference with respect to the thicknesses of other sections, each thickness is preferably about 1.0 mm or more and more preferably about 1.5 mm or more. The thickness of each section is preferably about 3.0 mm or less and more preferably about 2.5 mm or less.

The face member 11 a can be formed either by forging or casting. As material of the face member 11, titanium, titanium alloy or stainless steel may be used. Preferably, the volume of the golf club head 1 is about 100 cc or more, more preferably about 150 cc or more. On the other hand, the volume of the golf club head 1 is preferably about 500 cc or less and more preferably about 460 cc or less. Furthermore, the weight of the golf club head 1 is preferably about 170 g or more and more preferably about 175 g or more. On the other hand, the weight of the golf club head 1 is preferably about 250 g or less and more preferably about 245 g or less.

FIGS. 7-10 show sectional views of other examples of the first groove 50. In FIG. 7, the section of the first groove 50 is of an inverted trapezoid in which its upper base is longer than its lower base. Referring to FIG. 8, the section of the first groove 50 is U-shaped. In FIG. 9, the section of the first groove 50 is of an inverted triangle. In FIG. 10, the section of the first groove 50 is substantially semicircular. Although in FIGS. 4, 7, and 8, the top face of each rib having the maximum height T_(R) has a specific area, the top face area of the ribs having the maximum height T_(R) shown in FIGS. 9 and 10 is substantially zero.

As shown in FIGS. 8 and 10, the height of the rib decreases gradually as it goes from the top face of the rib 12 toward the heel-sole section 19 and the toe-sole section 17. Portions of the rib 12 which come into contact with the sections 19 and 17 are formed into a curved shape so that the same rib 12 maintains smooth contact with the sections 19 and 17.

Although in the above-described embodiments, the reinforcement rib 14 is provided as shown in FIGS. 1 to 6, the present invention may contain no reinforcement rib as shown in FIG. 11. In a case in which no reinforcement rib is provided, preferably, joined portions of the adjacent first and second main ribs 12, 13 are formed into a smooth curved shape.

According to another embodiment, the height of the rib may be changed depending on its position instead of providing the rib with a groove. That is, in regard to the heights of the first and second main ribs 12, 13, the height on the sole side is set smaller than the height on the crown side. In the main ribs 12, 13, preferably, with respect to the intersection portion 15, the maximum height on the sole side is about 30-80% of the maximum height on the crown side. Furthermore, the height of the reinforcement rib 14 may be defined so that the height on the sole side is smaller than that on the crown side. In the reinforcement rib 14, preferably, with respect to the intersection portion 15, the maximum height on the sole side is about 30-80% of the maximum height on the crown side.

EXAMPLES Examples 1-1, 1-2 and Comparative Example 1

The face member of the present invention was produced and its coefficient of restitution (COR) was evaluated. In this example, a characteristic time (CT) was measured instead of actually measuring the COR value. The CT value is a quantitative value capable of measuring a spring effect of the face simply and at a high precision, which has been adopted by the US golf association (USGA) and Royal and Ancient Golf Club of St. Andrews (R&A) and can be measured with a portable pendulum machine approved by R&A Rules Limited. Because generally, the more the face is deflected, the smaller the energy loss is, so that the initial velocity of a ball is higher, the CT value expresses the deflection with a contact time of the ball and the face. Currently, its maximum limit is determined to be 257 (239 officially stipulated+allowance of 18) μec according to the rule.

The Example 1-1 presents a structure shown in FIG. 3, in which the rib height T_(R) of the rib was 0.8 mm and the depth of the grooves 50 to 52 was 0.6 mm. According to the Example 1-2, the depth of the grooves 50 to 52 was set to 0.4 mm. On the other hand, for comparison, the Comparative Example 1 without any groove in the rib was produced. FIG. 12 shows a sectional view of the first main rib 12 according to the Comparative Example 1. The second main rib 13 and the reinforcement rib 14 were also provided with the same sectional shape as in FIG. 12. In the Examples 1-1 and 1-2 and the Comparative Example 1, the height of the first main rib 12 and the second main rib 13 was set to 0.8 mm and the height of the intersection portion was set to 1.2 mm. The reinforcement rib 14 as shown in FIG. 5 was provided. Furthermore, the thickness of the four sections, toe-crown section 16, toe-sole section 17, heel-crown section 18 and heel-sole section 19 was set to 2.4 mm.

As a common condition of the face member, the width and the height of the face member were set to 75 mm and 43 mm respectively, and the first and second main ribs were tilted in the same way as FIG. 1. The length of the reinforcement rib was set to 27 mm on the toe side, and 25 mm on the heel side. The width of the first and second main ribs was set to 9.5 mm and the width of the reinforcement rib was set to 7.1 mm. As a common condition of the golf club head, a titanium alloy (Ti-6Al-4V) was employed for material of the face member, the head volume was set to 460 cc and the head weight was set to 190 g. Then, the thickness of the crown portion was set to 0.7 mm and the thickness of the sole portion and the side portion was set to 0.9 mm.

For the Examples 1-1, 1-2 and the Comparative Example 1, the CT value at a hitting point of the ball was measured. With regard to the hitting points of the ball, 15 hitting points, which are different in the vertical direction and the horizontal direction, were investigated as shown in FIG. 13. A hitting point 40 c in the center assumes hitting the ball at the sweet spot and was supposed to be within the intersection portion of the face member. The other fourteen hitting points assume hitting the ball off the sweet spot. Positions 10 mm away from the central hitting point 40 c toward the toe side and the heel side are assumed to be hitting points 40 b, 40 d, respectively, and positions 10 mm further away toward the toe side and the heel side are assumed to be hitting points 40 a, 40 e, respectively. Positions 10 mm away from these five hitting points 40 a to 40 e toward the crown side and the sole side are assumed to be 40 aH to 40 eH and 40 aL to 40 eL respectively.

Of the above-described 15 hitting points, hitting points 40 bH and 40 dL are located on the first main rib 12 and hitting points 40 dH and 40 bL are located on the second main rib 13.

Under the above-described condition, the CT values of respective hitting points of the Examples 1-1, 1-2 and the Comparative Example 1 were measured. Tables 1 to 3 show the results. Tables 1 to 3 show a percentage of the CT values of other hitting points with respect to the CT values of the central hitting point 40 c regarding the Examples 1-1, 1-2 and the Comparative Example 1. FIGS. 14 to 16 show distribution maps of the CT values on the face member obtained by computer simulation based on these results. With the position of the central hitting point 40 c assumed to be 0 mm, in Tables 1 to 6 and FIGS. 14 to 16, a distance toward the heel side and the crown side is expressed as positive and a distance toward the toe side and the sole side is expressed as negative.

TABLE 1 Percentage of CT value in Example 1-1 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 97% 99% 96% 99% 91% Vertical 0 101% 105% 100% 103% 97% center 10 mm down −10 88% 97% 100% 91% 75%

TABLE 2 Percentage of CT value in Example 1-2 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 96% 99% 97% 99% 92% Vertical 0 100% 104% 100% 102% 97% center 10 mm down −10 85% 95% 98% 89% 75%

TABLE 3 Percentage of CT value in Comparative Example 1 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 98% 101% 98% 100% 93% Vertical 0 101% 105% 100% 102% 98% center 10 mm down −10 84% 91% 94% 88% 75%

In regard to the CT value of the face member (Example 1-1) provided with a rib having a groove 0.6 mm deep as shown in FIG. 14, the CT value on the sole side is higher than a face member (Comparative Example 1) provided with a rib having no groove as shown in FIG. 16, so that a face portion area having a CT value similar to that of the hitting point 40 c is greater. Furthermore, the CT value of a face member (Example 1-2) provided with a rib having a groove 0.4 mm deep as shown in FIG. 15 is higher than the Example 1-1, so that a distribution of the CT values is uniform.

Examples 2-1, 2-2, 2-3 and Comparative Example 2

In the Example 2-1, the height of the intersection portion 15 was set to 1.2 mm and the maximum height on the crown side of the first main rib 12 and the second main rib 13 was set to 1.0 mm. On the other hand, the maximum height on the sole side of the first main rib 12 and the second main rib 13 was set to 0.7 mm. In regard to the reinforcement rib 14, the maximum height on the crown side was set to 1.1 mm and the maximum height on the sole side was set to 1.0 mm. The thickness of the four sections 16 to 19 was set to 2.4 mm.

In the Example 2-2, the thickness of the toe-crown section 16 was set to 2.4 mm and the thickness of the toe-sole section 17 was set to 1.9 mm. Then, the thickness of the heel-crown section 18 was set to 2.3 mm and the thickness of the heel-sole section 19 was set to 2.4 mm. Other conditions were set to the same as the Example 2-1.

In the Example 2-3, no reinforcement rib 14 is provided and the first main rib 12, the second main rib 13, the first groove 50 and the second groove 51 were set to the same as the Example 2-1. The thickness of the four sections 16 to 19 were set to the same as the Example 2-2.

In the Comparative Example 2, the maximum heights of the first main rib 12, the second main rib 13 and the reinforcement rib 14 were set to 1.2 mm. The thickness of the four sections 16 to 19 was set to 2.4 mm. All ribs had no groove.

For the Examples 2-1 to 2-3 and the Comparative Example 2, the CT values of respective hitting points in FIG. 12 were measured under the above-described conditions. Tables 4 to 7 show the results. Tables 4 to 7 show a percentage of the CT values of other hitting points when the CT value of the central hitting point 40 c is assumed to be 100% in the Examples 2-1 to 2-3 and the Comparative Example 2. With the position of the central hitting point 40 c assumed to be 0 mm, in Tables 4 to 7, a distance toward the heel side and the crown side is expressed as positive and a distance toward the toe side and the sole side is expressed as negative.

TABLE 4 Percentage of CT value in Example 2-1 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 95% 98% 95% 97% 97% Vertical 0 99% 100% 100% 105% 96% center 10 mm down −10 83% 94% 94% 94% 82%

TABLE 5 Percentage of CT value in Example 2-2 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 96% 100% 98% 99% 99% Vertical 0 99% 103% 100% 101% 99% center 10 mm down −10 88% 96% 97% 98% 83%

TABLE 6 Percentage of CT value in Example 2-3 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 105% 100% 98% 99% 97% Vertical 0 102% 103% 100% 103% 103% center 10 mm down −10 88% 96% 98% 98% 92%

TABLE 7 Percentage of CT value in Comparative Example 2 20 mm 10 mm Horizontal 10 mm 20 mm to toe to toe center to heel to heel −20 −10 0 10 20 10 mm up 10 94% 95% 94% 96% 96% Vertical 0 94% 99% 100% 99% 94% center 10 mm down −10 83% 91% 92% 89% 76%

As is evident from Tables 4 to 7, the CT values of the Examples 2-1 to 2-3 are higher than the CT values of the Comparative Example 2, so that the distribution thereof is more uniform. In particular, the CT values of the four hitting points 40 bH, 40 dH, 40 bL, 40 dL on the ribs in the Examples 2-1 to 2-3 are higher than the CT values of the Comparative Example 2. 

What is claimed is:
 1. A golf club head having a hollow internal structure, the golf club head comprising: a face portion having a hitting surface; and first and second main ribs disposed inside the face portion, wherein the first main rib is extended from a crown side to a sole side and the second main rib is extended from a hosel side to a toe side of the sole, and the first and second main ribs intersect with each other at an intersection portion, and the first and the second main ribs are so constructed that stiffness of the sole side is lower than that of the crown side.
 2. The golf club head according to claim 1, wherein a first groove is provided from the intersection portion of the first main rib up to the sole side, and the depth of the first groove is not more than about ¾ of the maximum height of the first main rib, and a second groove is provided from the intersection portion of the second main rib up to the toe side, and the depth of the second groove is not more than about ¾ of the maximum height of the second main rib.
 3. The golf club head according to claim 1, wherein the height of the first and second main rib is about 0.5 mm to about 1.5 mm.
 4. The golf club head according to claim 1, wherein the height of the first and second main ribs is smaller on the sole side than on the crown side.
 5. The golf club head according to claim 1, wherein the width of the first and second main ribs is about 8 mm to about 14 mm.
 6. The golf club head according to claim 1, further comprising: a reinforcement rib which is disposed inside the face portion and extends from the intersection portion toward an end of the face portion, wherein the height of the reinforcement rib is decreased gradually from the intersection portion toward the end, and the reinforcement portion is formed part of the way to the end of the face portion. 